Apparatus for consolidating metal powders



0ct.'21, 1941. c. HARDY APPARATUS FOR CONSOLIDATING METAL POWDERSOriginal Filed Dec. -l5, 1937 Vazwum am a T N W M W a a -or both, andaims to angle of repose, so that it is Patented Oct. 21, 1941 CharlesHardy,

APPARATUS FOR CONSOLIDATING METAL POWDERS Pelham, N. Y., MetallurgicalCorporation, New York, N.

assignor to Hardy Y., a

corporation of Delaware Original application December 15,

and t 119,898. Divided i938, Serial No. 206,146

3 Claims.

This invention relates to powder metallurgy and particularly toapparatus and processes in which coherent objects are formedbysubjecting metal powders to compression or heat treatment such apparatusand processes and in such objects.

This application is a division of my co-pending application Serial No.179,898, filed December 15, 1937.

In the heretofore customary art of powder metallurgy, metal powders havebeen placed in a mold under ordinary atmospheric conditions (andconsequently containing entrapped air) and subjected to heating or tocompression or to both to form a coherent mass. Difiiculties have beenencountered in such practice. The metal powders do not fiow readilythrough small orifices or into confined spaces and have a relativelyhigh difiicult to fill the mold completely, especially when it is ofcomplex shape. This leads to the formation of objects which do notconform to the mold in all respects, and which cannot be used for theirintended purpose, especially when accurate configuration is essential.Morever, expulsion of the entrained air or other gas from the powdersduring compression not only-requires the use of very high compressiveforce, but also brings about stratification and the development ofplanes of weakness through the object, usually substantiallyperpendicular to the direction in which the force is applied.

Asa result of my investigations I have discovered that theaforementioned difliculties can be avoided in large measure byconducting the operation in vacuo, i. e., at pressures substantiallyless than atmospheric so that the proportion of air or other gas presentin the powder mass is substantially lessened. I have found that metalpowders which will not flow at all or at best only slowly and have ahigh angle of repose under atmospheric conditions, will flow readily andhave a very fiat angle of repose when the air or other gases entrainedin the interstices between the powder particles are evacuated, at leastin part. v Hereinafter powders in such an environment are somet esreferred to as evacuated. Generally speaking, the finer the particlesize of the powders, the greater is the increase in flow provideimprovements in treatment operations are 1937, Serial No. hisapplication May 5,

rate of the powder when evacuated. I have applied this discovery to moldfilling operations and find that when metal powders in an evacuatedcondition are introduced into an evacuated mold, the speed of operationis greatly increased, the powder mass fills and conforms to the moldwith substantial perfection, and the mass in the mold is more compactthan when the gases entrained at atmospheric pressures are present.

There are, therefore, advantages to filling the mold under conditions ofreduced gas pressure even though subsequent compression or heat notconducted under such conditions. However, further advantages accrue ifthe powder in the mold is kept evacuated during compression, in that theforce necessary to achieve any desired degree of densityin the resultingobject is only a small fraction of that necessary when gases are presentin the powder mass. Moreover, stratification and consequent developmentof planes of weakness during compression or subsequent heat treatment iseffectively prevented, probably due to the fact that the homogeneity ofthe powder mass undergoing com ression is not disturbed by gas which isbeing expelled.

My invention therefore contemplates the improvement in processesinvolving the filling of a mold with metal powder and its subsequenttreatment to form a coherent mass which comprises filling the mold afterthe mold or the powder to be introduced, and preferably both; have beenevacuated at least in part, whereby the rate of flow of powder into themold is increased and the mold is filled more completely with thepowder.

My invention also contemplates the compression of metal powder in themold after gases entrained in the powder mass have been evacuated, atleast in part, whereby consolidation of the powders is accomplished witha lower compressive force and the development of planes of weakness inthe resultant metal object is effectively prevented. The above describedprocess preferably is practiced in apparatus of my invention whichcomprises in combination a mold, a piston fitted in said mold. andslidable in the mold for compressing metal powder in the mold, a vacuumline connected .to the mold whereby the mold may be evacuated, filtermeans disposed in the vacuum line, a hopper, a conduit connected to saidhopgree of exhaustion may to the mold, a metal powder measuring chamberin said conduit, and a'seco'nd vacuum line connected to the measuringchamber whereby 1 the measuring chamber may be evacuated. These andother aspects of my invention will be understood thoroughly in the lightof the following detailed description of my presently preferredpractice, taken in conjunction with the accompanying drawing in which:

Fig. 1 illustrates diagrammatically apparatus of my invention for use insuch practice; and

Fig. 2 illustrates a modified form of the apparatus of Fig. 1.

Referring now to Fig. 1, it will be seen that the apparatus comprises avertically-disposed mold III of any desired shape in which is fitted avertically slidable piston H for compressing metal powders therein.Contrary to heretofore customary practice in which sufficient clearancewas left between piston and mold to permit the escape of gas, the pistonII should fit the mold with sufficient precision to insure againstleakage of gas into the mold, and incidentally, to prevent the formationof fins on the object due to powder which game between the wall of themold and the Dis- A steeply inclined conduit I 2 with an upperportion ofthe mold bottom of a hopper l3 for supplying to the mold. Valves l4, l5are positioned in the communicates ment), against collapse is created inthe hopper. by a tightly fitted but removable top I! and an annulargasket I8 of yieldable material.

' A vacuum line l9 communicates with a lower portion of the mold,preferably through a porous metal block 20 which conforms to the innersurface of the mold. A valve 2| is provided in the between the mold andthe valve.

A second vacuum line 24 communicates with the upper portion of thehopper, preferably at a point above the level for metal powder therein.A valve 25 is provided in the second vacuum line for controlling therate and degree of exhaustion of gases from the hopper. A manometer 26containing a mercury column 21 may be attached to the second vacuumline, preferably at a point betweenthe valve and the hopper so that thedebe determined by the operator.

A third vacuum line 28 is connected to an upper portion of the chamberl6, preferably through the porous metal block 29, so as to insure that avacuum is maintained in the measuring chamber.

It is convenient is compressed in the clearance and with the to connectthe third vacuum line to the second vacuum line at a point between thehopper and the valve 25.

A vacuum pump 30 or other apparatus for sucking gas out of the mold andout of the hopper and measuring chamber, is provided.

To facilitate movement of metal powder from the hopper through themeasuring chamber into the mold and to compact the powder in the moldprior to application of compressive force by means of the piston, it isdesirable to provide vibrating hammers 3|, 32, positioned respectivelyagainst the outer walls of the hopper and the mold.

The manometers should contain columns of mercury or other liquidsufliciently high to insure against breaking the seals in the manometerswhen the apparatus is placed under vacuum. In the case of operationsconducted under sea level conditions with mercury in the manometers, thecolumns should be longer than 760 mm.

In the event that the metal powders to be compressed are prepared readyfor use 'at a distance from the apparatus, say in another plant, it isconvenient to place the powder immediately after preparation into asealed container, from which the gas contained by the powders is thenexhausted at least partially. In this way, the metal powders are ingstorage. Moreover, time is saved in that the powders are already in anexhaustedcondition when introduced into the hopper, so that little or noadditional removal of gas in the hopper is necessary.

' the top of the hopper,

- tering the vacuum In the case in which the metal powders are deliveredready for use in a sealed and exhausted container, the container itselfis used in place of the top I! to seal the upper portion of the hopper.A container 33 can be constructed as in Fig. 2 so that when inverted,its top fits tightly against the gasket I 8. With the container in placeon hopper may be ruptured by means of a spear 35,

fastened on the upper inside end of a lever 36 which projects throughthe wall of the hopper in a sealed joint 31', say a stufilng box. Bypressing down on the outer end of the lever, the spear is forced uptorupture the top of the can or other container and the powders are thenfree to run into the hopper.

Assuming that the metal powder, preferably in a dry condition, is inplace in the sealed hopper, with the lower valve [4 closed, theoperation of the apparatus is as follows:

Both the mold and the hopper are evacuated with respect to gases.Preferably a high vacuum, say that equivalent to 750 mm. of mercury in amanometer under sea level conditions (absolute pressure of 10 mm. Hg) ispermitted to develop in both hopper and mold. With the measuring chamberfull of powder, the upper valve I 5 is closed. The valve I4 is thenopened and the batch of powder from the measuring chamber is allowed torun into the mold. The lower valve is then closed and the piston isforced down to compress the metal powder in the mold into a mass of therequired shape and density. Any gas expelled from the mold duringcompression is permitted to escape through the vacuum line l9, whichcommunicates with the mold near the bottom thereof, so that the loweredpiston will not shut it off. Powder is prevented from enlines I 9 and 28by the porous blocks 20 and 29.

Following compression, the valve 2| is closed;

the compressed mass is removed from the mold;

protected from oxidation durthe inverted top of the- -weld the particlestogether according to any of the conventional methods, say bysin'tering. The sintering or other heating operation need not beconducted under vacuum, although it is desirable to employ a neutral orreducing atmosphere.

In the event that the powder is not supplied ready for use in anevacuated container, it is dumped into the hopper. The top I! is thenplaced on the hopper to seal it and with hopper, measuring chamber andmold in an evacuated condition, the operation is conducted as describedhereinbefore.

The operation may also be conducted without placing the hopper under thevacuum. In such case the mold is exhausted as described hereinbefore.The valve II is closed and the valv i is open to permit powder to enterthe measuring chambe after which the valve I5 is closed. The powder inthe measuring chamber may then be freed from entrained gas by means ofthe vacuum line 28 or it may be introduced into the mold while itcontains the gas which it entrapped under atmospheric pressures. If thelatter procedure is followed the gas enters the mold and should bewithdrawn through the vacuum line l9 prior to compression of the powderin the mold. This practice is slower and is not so satisfactory as thatdescribed previously.

The speed and thoroughness with which the mold is filled, and the degreeof compactness obtainable in the powder before the piston is applied toit may be increased by vibrating the mold or the hopper or both by meansof the oscillating hammers 3| and 32 disposed respectively against thehopper and the mold.

The degree of vacuum to be employed depends upon the fineness of themetal powder, the degree of porosity or of density desired in thecompressed mass, and upon commercial considerations. Generally speaking,some advantage accrues to any operation in which the mold is filled orthe powder is compressed while the powder mass contains less gas than itwould entrain under normal atmospheric conditions.' However, it isrelatively easy to obtain in the apparatus a vacuum equivalent to anabsolute pressure of 10 mm. Hg (1. e. with. a manometer reading of 750mm. Hg under sea level conditions). I prefer, therefore, to operate withthe vacuum as high as this or higher.

As indicated'hereinbeiore the finer the metal powder the greater are thedifflculties in getting it to flow under ordinary atmosphericconditions, and the greater is the increase in fiow rate of the metalpowder and of the compactness which the powder will attain whenevacuated. The increase in flow rate is illustrated by the followingtests:

Dry copper powders were placed in a hopper having a valved orifice aboutV8" in diameter in the bottom opening into a reservoir below the hopper.Both reservoir and hopper were provided with vacuum connections so thatthey could be evacuated. In the first instance, the flow rate of eachtype of powder through the orifice was measured under atmosphericpressure,

'i. e., with atmospheric pressure (760 mm. Hg) in both hopper andreservoir. This was compared with the flow rate of the same powder invacuo,

i. e., with both hopper and reservoir exhausted to an absolute pressureof 4 mm. Hg, as indicated by a manometer reading of 756 mm. Hg. Thefollowing results were obtained:

Flow data Type of powder 10. 5 cm. 5 es. 0

flowing through A," diameter Grams powder orifice per minute I With gaspressure corresponding to 760 mm. Hg on both sides of orifice.

-11 With gas pressure corresponding to 4 mm. Hg on both sides oforifice.

382 None Tyler scale. d Minus 200, plus 325 mesh.

As the results show, a remarkable increase in the flow rate of coarsemetal powder'iType B) througha small orifice is obtained in vacuo, butthe increase in flow rate over that obtainable under atmosphericconditions is greater with a finer powder (Type R), while very finepowder (Type C) which will not flow at all through an orifice underatmospheric conditions, flows rapidly through the same orifice in vacuo.

Metal powders, especially when dry, can be compacted to a greater extentin vacuum when at least a portion ot the gas which they entrain underatmospheric conditions has been removed, even though no greatcompressing force i applied. Moreover, vibration oi the powders in vacuoaids considerably in increasing the flow rate of the powder and also thedegree of compactness obtainable. Generally speaking, the finer thepowder, the more compact it becomes when entrapped gases have beenremoved, even partially. With. fine metal powders, say, Type C,

the volume occupied by the powder mass dee creases and the apparentdensity of the powder mass increases by at least 20% in 'a vacuumequivalent to an absolute pressure of 3 mm. Hg. However, a greaterdecrease in the volume occupied by a mass of even coarser powders, say,Type B, can be obtained if the powder is shaken or vibrated in anevacuated space. The increase in compactness of the powder, thusobtained before compression by a piston in a mold, is of assistance inmaking accurately formed objects. Moreover, it permits niore'metalpowder to be placed in a space prior to compression, and thus permitslarger articles to be manufactured in a given press. obtaining increaseddensity with the application of a minimum of compressive force.

However, the greatest saving in compressive force is due to theelimination of the cushioning effect 01 the gas in the mold in whichcompression takes place. It might be thought that the onlysaving incompressive force obtainable by removing entrapped gas from the powderssubjected to compression, would be at best about 15 lbs. per' squareinch, since this is the maximum force exerted by the gas underatmospheric conditions. However, I have found that a much greater savingin compressive force results. For example, the density obtainable bycompressing, under a force of 25 tons per square inch, metal powders(Type 0) containing the air which these It is also an important actorinpowders entrap under normal atmospheric conditions, is also obtainablewith a force of only tons per square inchin an environment having anabsolute pressure of 3 mm. Hg.- This represents a saving ofapproximately 80% in compressive force, and power.

If desired, the degree of vacuum obtaining in the mold prior tocompression of the powders can be controlled to regulate the density anddegree of porosity of the compressed object, the compressive forcesapplied by the piston being held substantially constant. Thus a presscan be set to apply a maximum force of say ten tons per square inch, anda dense body of small but controlled porosity obtained by exhausting thegas from the powders with a or a more porous body can be obtainedthrough the application of the but with a lesser degree ofvacuum andconsequent increase in the amount of gas entrained in the powderssubjected to compression.

Almost any metal powders or powder mixtures can be employed in thepractice of my invention. Thus, mixtures of copper powder, tin powderand powdered graphite, such as is used for making bearings, may beemployed. Alloy steel mixtures containing iron powder, finely-dividedcarbon and powdered alloy ingredients such as silicon, chromium, nickel,vanadium, tungsten, and the like, may be used.

The powders should be relatively dry in order to in the .mold prior tocompression. However, binders such as powdered metallic soaps may beemployed because these materials do not interfere markedly with the flowrates of powders in which they are included.

The metal powder mixture, for example, mixtures of powdered copper, tinand graphite, for use in bearing manufacture, can be prepared at adistance and shipped in evacuated containers I as describedhereinbefore.

The advantages or my invention may be recapitulated as follows:

(1) Increased speed of mold filling andconsequent acceleration ofoperations and increased production for a press.

(2) Increased accuracy of configuration in the pressed article,especially when the mold is of complicated shape. Y

(3) Elimination of planes of weakness and high degree of vacuum.

same compressive force obtain maximum flow rate and compactnesselimination of lack of homogeneity in structure and density of thefinished article.

(4) Greater compactness of powders prior to compression, leading to theproduction of longer objects in a given press.

(5) Reduction of oxidation ders prior to and during treatment, withconsequent improved welding together of the particles.

(6) Lower compressive force to obtain a product of given density,thereby increasing the size of objects obtainable in a given press anddecreasing power consumption.

I claim:

1.' In apparatus for compressing metal powder the combination whichcomprises a mold, a piston fitted in and slidable in the mold, a vacuumline connected to the mold, filter means disposed in the vacuum line, ahopper, .means for sealing the hopper, a second vacuum line connected tosaid hopper, a conduit connected to the mold and to the hopper andextending downwardly from the hopper to the mold, a metalpowdermeasuring chamber in said conduit, and a third vacuum lineconnected to the measuring chamher.

2. In apparatus for compressing metal powder the combination whichcomprises a mold, a piston fitted in said mold and slidable in the moldfor compressing metal powder in the mold, a vacuum'line connected to themold whereby the mold may be evacuated, filter means disposed in thevacuum line, a hopper, a conduit connected to said hopper and extendingdownwardly from the hopper to the mold, ametal powder measuring chamberin said conduit, and a second vacuum line connected to the measuringchamber whereby the measuring chamber may be evacuated.

3. In apparatus for compressing metal powder the combination whichcomprises a mold, means for compressing metal powder vin said mold,means for maintaining a vacuum in said mold prior to and duringcompression, a hopper, an airtight container for metal powder, means forsealing the container to the hopper, means for creating a vacuum in saidhopper, a conduit connected to the hopper and to the mold to permitmetal powder to pass from the hopper to the mold, and means disposedwithin the hopper for piercing a wall of the airtight container which issealed to the hopper. CHARLES HARDY.

of the metal pow-

